Energy self-sufficient households with photovoltaics and electric vehicles are feasible in temperate climate

We explore this in more detail in Fig 5, showing the relative share of the area we assume to be available used in each case as a function of scenario, and comparing 22.1% and 27.2% roof- top PV efficiencies. Rooftop area is always used first because of the higher efficiencies com- pared to facade PV. With an efficiency of 22.1%, the available facade area in SFB cases is sufficient, except for case SRCR, which can also be seen in Fig 3 where it is the only case out- side the true zero energy building boundary at 22.1% efficiency. Where cases reach beyond the grey shaded region, they fail to fulfill our design requirements. However, they are not at their Fig 4. Cases with SFBs (left) and MFBs (right) considering backup hydrogen production in the size 1.75 times the optimized amount in net negative months. Values above zero net energy availability indicate cases that are successfully true zero energy buildings throughout the year. Values below this line indicate failed cases. The PV module efficiency is for rooftop PV systems; facade PV system efficiency tracks that of rooftop PV efficiency as indicated in the methods section above. https://doi.org/10.1371/journal.pone.0227368.g004 Table 5. Battery and hydrogen tank sizes as well as area covered by the PV system per case. Required rooftop and facade area are given to fulfil the energy demand with the assumption of a rooftop PV efficiency of 27.2% and facade PV efficiency. Cases marked with � are considered to exceed our limits for PV area and thus not able to be fully self-sufficient.

Battery size (kWh) Hydrogen tank size (m3) Rooftop PV area (m2) Facade PV area (m2) SNPU 38.6 9.0 46.7 0 SNPR 45.8 10.7 55.1 0 SNCU 44.9 10.4 54.2 0 SNCR 52.1 12.1 62.7 0 SRPU 39.4 9.2 48.2 0 SRPR 46.6 10.8 56.6 0 SRCU 45.7 10.6 55.7 0 SRCR 52.9 12.3 57.0 10.3 MNPU 162.5 37.8 200.0 0 MNPR 191.9 44.7 219.7 21.1 MNCU 185.6 43.2 219.7 11.7 MNCR 215.0 50.0 219.7 61.1 MRPU� 164.5 38.3 153.8 71.9 MRPR� 193.9 45.2 153.8 121.3 MRCU� 187.6 43.7 153.8 112.0 MRCR� 217.0 50.5 153.8 161.3 https://doi.org/10.1371/journal.pone.0227368.t005 Energy self-sufficient households with photovoltaics and electric vehicles are feasible in temperate climate PLOS ONE | https://doi.org/10.1371/journal.pone.0227368 March 4, 2020 13 / 25